Continuously variable transmission devices that include a toroidal continuously variable transmission are used as automatic transmission devices for vehicles, including automobiles. In this continuously variable transmission device, in order to increase the variable range of the transmission ratio, the toroidal continuously variable transmission may also be combined with a differential gear unit such as a planetary gear transmission. For example, JP 2011-174486 (A) and JP 2012-002330 (A) disclose a continuously variable transmission device that includes a mode in which the rotating state of the output shaft is switched between forward and reverse by passing through a so-called geared neutral state (GN) in which the rotating state of the output shaft is stopped while allowing the input shaft to continue to rotate as is in one direction.
FIG. 7 and FIG. 8 illustrate a conventional continuously variable transmission device that includes a mode that makes it possible to achieve a geared neutral state. FIG. 7 is a block diagram of a continuously variable transmission device and FIG. 8 illustrates a hydraulic circuit for controlling a continuously variable transmission. The output from the engine 1 is inputted to the main shaft 3 by way of a damper 2. The power that is transmitted to the main shaft 3 is then transmitted directly or by way of a toroidal continuously variable transmission device 4 to a planetary gear transmission 5 as a differential gear unit. The differential component of the component members of the planetary gear transmission 5 is output to the output shaft 9 by way of a clutch device 6 that includes a low-speed clutch 7 and a high-speed clutch 8 (see FIG. 8).
The toroidal continuously variable transmission 4 of the continuously variable transmission device includes an input disk 10, an output disk 11, plural power rollers 12, plural trunnions (not illustrated in the figure), an actuator 13 (see FIG. 8), a pressure device 14, and a transmission ratio control unit 15. The input disk 10 and output disk 11, as disclosed in detail in JP 2013-002330 (A), respectively include an axial side surface which is constituted of a toroidal curved surface, the axial side surfaces of the input disk 10 and output disk 11 facing each other, and the input disk 10 and output disk 11 are arranged so as to be concentric with each other and so as to be capable of relative rotation. Each of the power rollers 12 is supported by a corresponding trunnion so as to be able to rotate, is held between the axial side surfaces of the input disk 10 and output disk 11, and transmits power (force and torque) between the input disk 10 and output disk 11. The actuator 13 is a hydraulic actuator, and changes the transmission ratio between the input disk 10 and the output disk 11 by causing the trunnions that support the power rollers 12 to be displaced in the axial direction of pivot shafts that are provided on both end sections of the trunnions. The pressure device 14 is a hydraulic pressure device, and presses the input disk 10 and output disk 11 in opposite directions approaching each other. The transmission ratio control unit 15 controls the displacement direction and displacement amount of the actuator 13 in order to set the transmission ratio between the input disk 10 and output disk 11 to a desired value.
The transmission ratio control unit 15 includes a controller (ECU) 16; a stepping motor 17, a line pressure control solenoid valve 18, a pressure force control solenoid valve 19, and a mode switching solenoid valve 20, that are switched based on a control signal from the controller 16; and a control valve device 21 the operating state of which is switched by the stepping motor 17 and the mode switching solenoid valve 20. The control valve device 21 includes a transmission ratio control valve 22, a low-speed clutch control valve 23, and a high-speed clutch control valve 24 (see FIG. 8). The transmission ratio control valve 22 controls the supply or discharge of pressure oil to the actuator 13. The low-speed clutch control valve 23 and the high-speed clutch control valve 24 correspond to the mode switching solenoid valve 20, and switch the state of the hydraulic pressure to the low-speed clutch 7 and high-speed clutch 8.
An oil supply pump 25 is driven by power that is outputted from the damper 2, and pressure oil that is discharged from the oil supply pump 25 is fed to the control valve device 21 and the pressure device 14. In other words, pressure oil that is taken in from an oil reservoir 26 (see FIG. 8) and discharged from the oil-supply pump 25 is adjusted to a specified pressure by a pressure force adjustment valve 27 (see FIG. 8). The pressure force adjustment valve 27 adjusts the injection-valve opening pressure according to the hydraulic pressure which corresponds to the difference in hydraulic pressure (differential pressure) between a pair of hydraulic pressure chambers which are provided on both sides of a piston in the actuator 13, and introduction of hydraulic pressure based on the opening and closing of the line pressure control solenoid valve 18 that is controlled by an instruction from the controller 16. Then, taking this injection-valve opening pressure to be the maximum value, the pressure force control solenoid valve 19 regulates the pressure force generated by the pressure device 14 to an optimal value according to the operating state at that instant.
The hydraulic pressure that is adjusted by the line pressure control solenoid valve 18 and pressure force adjustment valve 27 is further adjusted (reduced) to a specified pressure by a reducing valve 28, and the hydraulic pressure is fed to inside the hydraulic pressure chamber of the low-speed clutch 7 or high-speed clutch 8 by way of the low-speed clutch control valve 23 or high-speed clutch control valve 24. The low-speed clutch 7 is connected in order to realize a low-speed mode in which the reduction ratio is increased, or the transmission ratio is made infinitely large (geared neutral state), and is disconnected in order to realize a high-speed mode in which the reduction ratio is decreased. On the other hand, the high-speed clutch 8 is disconnected in order to realize the low-speed mode, and is connected in order to realize the high-speed mode. The state of supplying or discharging pressure oil to the low-speed clutch 7 and high-speed clutch 8 is switched according to switching of the mode switching solenoid valve 20. When switching between the low-speed mode and high-speed mode based on switching between the low-speed clutch 7 and high-speed clutch 8, the transmission ratio of the toroidal continuously variable transmission 4 is adjusted so that the transmission ratio (1/reduction ratio) of the overall continuously variable transmission device is the same in the low-speed mode and the high-speed mode.
Signals respectively indicating the rotational speed of the input disk 10, output disk 1 and output shaft 9 which are detected by the input disk rotation sensor 29, output disk rotation sensor 30 and output shaft rotation sensor 31 are inputted to the controller 16. Moreover, the controller 16 then exchanges signals with the engine controller 32. Furthermore, a transmission mode switching signal that indicates the connected or disconnected state of the low-speed clutch 7 and high-speed clutch 8, and a T/M selection position signal that indicates the operating position of the selection lever are inputted to the controller 16. In addition, a paddle shift signal for a manual gear change, a foot brake signal that indicates whether or not the brake pedal has been operated, and an accelerator pedal aperture signal that indicates the amount that the accelerator pedal has been pressed are inputted to the controller 16 by way of the engine controller 32.
FIG. 9 illustrates an example of the relationship between the speed ratio of the toroidal continuously variable transmission 4 and the speed ratio of the overall continuously variable transmission device. For example, in the low-speed mode in which the low-speed clutch 7 is connected and the high-speed clutch 8 is disconnected, as illustrated by the solid line a, as the transmission ratio of the toroidal continuously variable transmission 4 is changed to the reduced-speed side from a value in which the geared neutral state is realized (GN value, GN point), the transmission ratio of the overall continuously variable transmission device is changed from a stopped state (state of a transmission ratio of 0) to a direction in which speed is increased in the forward direction (+:forward rotation direction). Moreover, as the transmission ratio of the toroidal continuously variable transmission 4 is changed to the increased-speed side from the GN value, the transmission ratio of the overall continuously variable transmission device is changed from a stopped state to a direction in which speed is increased in the reverse direction (−: reverse rotation direction). On the other hand, in the high-speed mode in which the high-speed clutch 8 is connected and the low-speed clutch 7 is disconnected, as illustrated by the solid line β, as the transmission ratio of the toroidal continuously variable transmission 4 is changed to the increased speed side, the transmission ratio of the overall continuously variable transmission device is changed to a direction in which the speed increases in the forward direction.
Switching between the low-speed mode and high-speed mode, or in other words, disconnecting and connecting the low-speed clutch 7 and high-speed clutch 8 is performed at the intersecting point γ of the solid lines α and β. At the point γ, the transmission ratio in the low-speed mode state and the transmission ratio in the high-speed mode state coincide with each other. As disclosed in JP 2005-191486 (A) and JP 2009-197892 (A), when switching between the low-speed mode and the high-speed mode, the clutch that was not connected up to that point is connected, and for an instant, the low-speed clutch 7 and high-speed clutch 8 are simultaneously connected. After that, only the newly connected clutch that corresponds to the mode to be realized next remains connected, and the clutch that was connected up to that point is disconnected. By providing an instant in which the low-speed clutch 7 and the high-speed clutch 8 are simultaneously connected in this way, a pick-up response of the engine when switching modes is prevented, and it is possible to reduce transmission shock.
With this kind of continuously variable transmission device, in order to smoothly switch between modes, the transmission ratios of these modes of the continuously variable transmission device coinciding during the instant of switching between the low-speed mode and high-speed mode is a precondition. When the low-speed clutch 7 and high-speed clutch 8 are simultaneously connected in a state in which these transmission ratios do not coincide, an excessively large load is applied to the toroidal continuously variable transmission 4. More specifically, at the areas of rolling contact (traction areas) between the input disk 10 and output disk 11 and the power rollers 12, the circumferential speeds of the pairs of surfaces that come in rolling contact do not coincide with each other. As a result, large slippage (cross slipping) occurs at the areas of rolling contact, and the durability of the toroidal continuously variable transmission 4 is severely impaired. Furthermore, there is a possibility that the toroidal continuously variable transmission 4 will break in a short period of time, and that operation of the vehicle in which the continuously variable transmission device is mounted will become impossible.
When the speed of a vehicle in which this continuously variable transmission device is mounted suddenly changes, or in other words, when the vehicle suddenly accelerates or decelerates, it is necessary to switch between the low-speed mode and high-speed mode in a short amount of time. For example, during the sudden acceleration process, the low-speed clutch 7 that was connected up to that point remains connected, and the high-speed clutch 8 that was disconnected up to that point is connected for a short amount of time, then after a state in which both the low-speed clutch 7 and high-speed clutch 8 have been connected for a short amount of time, the low-speed clutch 7 that was connected up to that point is disconnected. During a sudden deceleration process, the opposite state is realized. In either case, connecting both the low-speed clutch 7 and high-speed clutch 8 at the same time occurs only during a state in which the transmission ratio of the toroidal continuously variable transmission 4 is the same in the low-speed mode and high-speed mode, however, is essential from the aspect of protecting the toroidal continuously variable transmission 4. On the other hand, in order to switch between the low-speed mode and high-speed mode in a short amount of time, preferably disconnecting and connecting the low-speed clutch 7 and high-speed clutch 8 while continuously changing the transmission ratio of the continuously variable transmission 4 is performed in a very short time.
However, in the case of a hydraulic clutch, a certain amount of time is required after a signal indicating that the hydraulic pressure inside the hydraulic pressure chamber should be set to a desired pressure in order to disconnect or connect the clutch is generated until the hydraulic pressure inside the hydraulic pressure chamber actually reaches that desired value, which cannot be avoided. When the length of this time is so long that it cannot be ignored when compared with the amount of time required for disconnecting and connecting the low-speed clutch 7 and high-speed clutch 8, harmful slipping will occur in the areas of rolling contact in the toroidal continuously variable transmission 4 when switching between the low-speed mode and high-speed mode, which becomes the cause of impaired durability of the toroidal continuously variable transmission 4.
In the case of a continuously variable transmission that is constructed by combining a toroidal continuously variable transmission and differential gear unit such as a planetary gear transmission, and that switches between a low-speed mode and high-speed mode by disconnecting and connecting a hydraulic low-speed clutch and high-speed clutch, this kind of problem occurs even when construction is not capable of achieving geared neutral. A continuously variable transmission called a power split such as disclosed in JP H11-236955 (A) in which transmission efficiency is improved by transmitting power by only a toroidal continuously variable transmission in the low-speed mode, and transmitting power by both a toroidal continuously variable transmission and a planetary gear transmission in the high-speed mode is known. In this kind of power split continuously variable transmission as well, a similar problem occurs when switching modes.
In the case of either construction of a continuously variable transmission device, when the torque that is transmitted by the continuously variable transmission device changes suddenly, there is a possibility that adjustment of the pressure generated by the pressure device 14 will not be able to keep up. For example, during sudden acceleration when the accelerator pedal is suddenly pressed a large amount, it is necessary to increase the aperture of the pressure force control solenoid valve 19, increase the hydraulic pressure introduced inside the hydraulic pressure chamber of the pressure device 14, and increase the surface pressure at the areas of rolling contract of the toroidal continuously variable transmission 4. However, even when adjusting the hydraulic pressure that is introduced inside the hydraulic pressure chamber of the pressure device 14 by the pressure adjustment valve 27, it takes a certain amount of time until the hydraulic pressure inside the hydraulic pressure chamber of the pressure device 14 is adjusted to a desired value. When this rise in hydraulic pressure does not keep up with the rise in the output torque of the engine, harmful slipping occurs at the areas of rolling contact of the toroidal continuously variable transmission 4, which becomes a cause of impaired durability of the toroidal continuously variable transmission 4.
When the pressure force generated by the pressure device 14 is excessively higher than a value that corresponds to the output torque of the engine, the loss at the areas of rolling contact of the toroidal continuously variable transmission 4 increases, however, harmful slipping does not occur at the areas of rolling contact. Therefore, it becomes particularly important that adjustment of the hydraulic pressure inside the hydraulic pressure chamber of the pressure device 14 be performed so that the pressure is increased quickly. In order for this, JP 2009-121530 (A) discloses performing control of the pressure force generated by the pressure device based on the torque generated by the engine instead of the torque that passes through the toroidal continuously variable transmission when the accelerator pedal is suddenly pressed a large amount. In this case, it is possible to eliminate the insufficient pressure force during sudden acceleration to a certain extent, however, preventing insufficient pressure force by speeding up the timing at which a signal is sent to the pressure force adjustment valve is not able to shorten the time required for the hydraulic pressure inside the hydraulic pressure chamber to rise after the signal has been sent to the pressure force adjustment valve.